Sectional fire door assembly

ABSTRACT

A door having horizontally hinged sections is supported upon reinforced track means for movement between an upright closed position and an open position. A counterbalance mechanism, which is mounted upon the wall above the opening, is connected to the door to counteract gravity. The counterbalance springs are connected to fusible link means which melts at a predetermined temperature and thereby reduces the tension on the springs so that the door will close under the force of gravity. Governor means is rendered operative when the fusible link is ruptured to control the closing movement of the door.

United States Patent Pemberton et al.

[is] 3,685,567 [451 Aug. 22, 1972 [54] SECTIONAL FIRE DOOR ASSEMBLY [72] lnventors: Paul E. Pemberton, 13327 Arawak, Dallas, Tex. 75234; John J. Luby, 303 N. Merrill Ave., Duncanville,

Tex. 751 16 [22] Filed: Sept. 18, 1969 [21] Appl. No.: 858,974

[52] US. Cl. ..160/8, 49/7, 160/191 [51] Int. Cl. ..E05l 15/20 [58] Field of Search ..160/7, 8, 9, 209, 40, 201, 160/191, 192,1

[56] References Cited UNITED STATES PATENTS 1,203,847 11/1916 Cahill ..160/9 1,992,006 2/1935 Greegor ..160/192 UX 2,012,336 8/1935 Blodgett ..160/9 2,059,833 11/1936 Winn ..160/9 2,257,484 9/1941 Rowe ..160/191 2,850,088 9/1958 Purdy ..160/188 2,923,541 2/1960 Gessell ..160/189 3,160,200 12/ 1964 McKee et a1. 160/189 3,559,716 2/1971 Loucks ..160/191 X 948,239 2/1910 McManus ..160/9 Cahill ..160/9 X Primary Examiner-Dennis L. Taylor AttorneyWoodhams, Blanchard and Flynn [57] ABSTRACT A door having horizontally hinged sections is supported upon reinforced track means for movement between an upright closed position and an open position. A counterbalance mechanism, which is mounted upon the wall above the opening, is connected to the door to counteract gravity. The counterbalance springs are connected to fusible link means which melts at a predetermined temperature and thereby reduces the tension on the springs so that the door will close under the force of gravity. Governor means is rendered operative when the fusible link is ruptured to control the closing movement of the door.

10 Claim, 17 having Figures Patented Aug. 22, 1972 3,685,557

5 Sheets-Sheet 1 mvsmons PAL/A i. PEMBZETOA/ ao/w 1/ mm Patented Aug. 22, 1972 3,685,567

5 Sheets-Sheet" 4 INVENTOR. P40! 5 P01454197 0/1/ 4/0///V J. ZUBV BY -r W QMW mam/[M2 SECTIONAL FIRE DOOR ASSEMBLY BACKGROUND OF THE INVENTION This application relates in general to a fire door assembly and, more particularly, to an upwardly acting door having horizontally hinged sections and a springbiased counterbalance connected to the door by means including a fusible link adapted to melt at a predetermined temperature and thereby reduce the tension on the spring so that the door can move into its closed position under the force of gravity.

For the most part, fire door assemblies have been provided in two different arrangements. In one arrangement, the door is supported by rollers upon a rail which is mounted upon and parallel with the wall above the door opening. The rail extends sidewardly beyond the door a distance approximately equal to the width of the door, and the rail often slopes downwardly toward the closed position. Accordingly, since the door is normally open when the building in which it is installed is being used, the wall space occupied by the opened fire door is unavailable for other use, such as shelving, windows and the like. Moreover, since the door must slide across the floor, its installation and use create a number of operational problems which are inherent in the door structure and, therefore, cannot be readily overcome, if at all.

For example, in order to provide a reasonably tight fit between the lower edge of the door and the threshold when the door is in the closed position, the supporting rail may be sloped. Accordingly, the door tends to wedge itself into the closed position, particularly if the door is relatively heavy and is closed firmly. This wedging effect is increased by the expansion of the door when it is exposed to heat. Thus, if allowance is made for such expansion, then there maybe a substantial space between the door and the floor when the door is in its normally closed position.

In order to avoid entrapment of persons having insufficient strength to unwedge a heavy door, an auxiliary escape door is often provided at another point in the wall or, in some instances, in the fire door itself. This arrangement creates the possibility of having the fire door closed and the auxiliary door open so that the purpose of the fire door is completely frustrated.

With the sidewardly sliding door arrangement, any change in the threshold, such as swelling during humid weather or the deposit of dirt on the threshold, can prevent the door from moving into its fully closed position, thereby leaving an opening along the leading edge of the door. More specifically, the slope of the doorsupporting rail must be gentle, such as less than 5, particularly with a heavy door, or it cannot be manually opened. In fact, even with a slope of 5, it is usually necessary to provide a counterbalance weight which is connected to the door by cables and pulleys which require the use of additional wall space. However, even with a slope of 5", a relatively small increase in the level of the threshold will cause the sidewardly sliding door to stop several inches short of closing the opening. Thus, the door must be made considerably wider than the width of the opening to ensure a full closing of the opening in case of any obstruction by the threshold, and this takes more wall space. Moreover, the sliding action of the door on the floor will eventually create a wear condition which cannot be avoided.

In order to avoid the foregoing problems, stops are sometimes placed on the wall for engagement by the leading edge of the door. However, this often results in a substantial space beneath the lower edge of the door through which smoke and fire can escape, especially if allowance is made for expansion of the door due to heat.

The effectiveness of the sidewardly sliding fire door is further reduced by the fact that the trailing edge of the door cannot be effectively sealed without considerable difficulty. That is, there is no convenient way in which the trailing edge of the door, which does not actually cross the opening, can be held tightly against the wall without using some auxiliary connection means, which would not be readily accessible from the other side of the door, if at all. Thus, even if the lower edge of the door is permitted to engage the threshold, at least the trailing edge of the door normally remains loose with respect to the wall adjacent the opening which the door is intended to cover. In an attempt to overcome this problem, the door is made substantially larger than the opening, which increases weight, cost and loss of wall space.

Also, it is virtually impossible to provide a sidewardly sliding door, which will close automatically under the force of gravity, without the supporting rail at a dangerous slope which would certainly require a powerdriven door operator to open the door. Without this slope, a power-driven door operator would be required for automatic closing in case of fire. Obviously, a failure of the door operator, as by fire damage, could prevent closing of the fire door.

A vertically sliding and one-piece fire door which would close automatically in case of fire, would be highly dangerous because of the guillotine efiect.

The other basic type of fire door is hinged upon the wall along one vertical edge of the door, and this type of door fiirther accentuates the problem of wasted space, particularly if the door is large. That is, under normal circustances, a semicircular swing space having a radius equal to the width of the door must be available where a sidewardly swinging door is used, which is the-main reason why they are mainly used for small openings. Automatic closing of the swinging fire door in case of fire would require a power-driven door operator. Swinging doors capable of withstanding the heat of a fire are necessarily heavy. Thus, it is at least impractical, and in some cases would be literally impossible, to support a large swinging fire door. That is, under many circumstances, even if the door were adequately braced to be supported by hinge means along one vertical edge thereof, the adjacent wall structure would be incapable of supporting such a load.

Moreover, in view of the fact that a swinging door must clear the floor during its swinging movement, suitable clearance must be provided between the lower edge of the door and the floor to allow for such swinging. Accordingly, special threshold means are required to provide a close seal between the floor and the door in the closed position. If a swinging door is of considerable width, any raising of the threshold would obstruct the proper closing of the door or wedge it shut. Moreover, if the heat'of the fire reaches the door first, the door might expand sufficiently to prevent closing or to jam shut and entrap people behind it.

Upwardly acting doors having a plurality of horizontally hinged sections have been used for many years on automobile garages, in commercial buildings and on aircraft hangers, for example. Much thought has been given in the past to the use of an upwardly acting sectional door as a fire door because it eliminates a prime problem with other doors, namely, storage of the door when it is open. The upwardly acting door is arranged to be stored in a normally unoccupied zone above the heads of personnel and equipment when the door is open. However, heretofore, use of the upwardly acting door as a fire door encountered two serious problems which seemed to be incapable of solution. First, it was not seen how the edges of the door could be encased to prevent the escape of smoke and fire therearound. Second, it was not seen how the spring-biased counterbalance means, which is used on most heavy doors to counteract the force of gravity, could be automatically released to permit the door to close by gravity in case of fire. This, of course, has been a feature desired but not previously obtained in any other type of conventional fire door presently used. Thus, there was no incentive to pursue automatic closing of the upwardly acting door until the other problem was solved.

Accordingly, a primary object of this invention is the provision of a fire door assembly including an upwardly acting door which will move automatically under the force of gravity from a raisedor open position into a substantially upright closed position, said assembly including guide means for preventing the escape of smoke or fire around substantially all edges of the door without interfering in the least with the normal operation of the door.

A further object of this invention is the provision of a fire door assembly, as aforesaid, which can be adapted 'for manual operation, either directly or with the aid of a chain hoist, or powered operation by means of a power-driven door operator.

A further ob ect of this invention is the provision of a fire door assembly, as aforesaid, in which the door can be opened and closed in a completely conventional manner at anytime prior to its automatic operation as a result of a fire or accidental tripping and which can be reset for normal operation after it is tripped to act automatically in a matter of minutes by maintenance pering door assembly embodying the invention and as seen from the interior of a building in which it is installed.

FIG. 2 is a broken, sectional view taken along the line IIII in FIG. 1.

' FIG. 3 is a sectional view taken along the line 111411 in FIG. 1.

FIG. 4 is a broken, sectional view taken along the line [VIV in no. 1.

FIG. 5 is a brokenand fragmentary, sectional view taken along the line VV in FIG. 1.

FIG. 6 is a broken, top view as seen from the line Vl-VI in FIG. 1.

FIG. 7 is a sectional view taken along the line VII -VII in FIG. 6.

FIG. 8 is a sectional view taken along the line VIII- VIII in FIG. 6.

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 6. I

FIG. 10 is a fragmentary and broken, sectional view taken along the line X-X in FIG. 1.

FIG. 11 is an enlarged fragment of the structure appearing in the upper left corner of FIG. 1.

FIG. 12 is an enlarged fragment of the structure appearing in FIG. 5. g

FIG. 13 is a sectional view taken along the line XIII- XIII in FIG. 11.

FIG. 14 is an enlarged fragment of FIG. 1 illustrating an alternate embodiment of the invention.

FIG. 15 is an end view of said alternate embodiment asviewed from the line XV-XV in FIG. 14.

FIG. 16 is a sectional view taken along the line XVI-XVI in FIG. 14.

FIG. 17 is a sectional view similar to that taken along the line VIII-VIII in FIG. 6, but disclosing a modified structure.

For convenience in description, the terms upper,- lower, left, right and terms of similar import will have reference to the door assembly and parts thereof as appearing in FIG. 1. The terms exterior or front and interior or rear" will have reference, respectively, to the left and right sides, respectively, of the door assembly and associated parts as appearing in FIG. 5. The terms inner," outer, and derivatives thereof will have reference to the geometric center of the door assembly and parts thereof.

SUMMARY OF INVENTION The objects and purposes of the invention have been 0 met by providing a door assembly having an upwardlyhorizontal, and a substantially uprifltt closed position either manually or by a power-driven door operator. Counterbalance mechanism, which is mounted upon the wall above the door opening therein, includes a spring-biased cable connected to the lower portion of the door for counteracting the force of gravity. In one form of the invention, where the door is manually I the door is opened and closed by a chain-driven device or a power-driven door operator, the fusible link is part of the connection between the chain or the operator and the counterbalance mechanism. Thus, rupture of the link disengages the counterbalance mechanism from the chain-driven device or door operator.

DETAILED DESCRIPTION The fire door assembly shown in FIG. 1 illustrates one preferred embodiment of the invention, wherein the door is manually raised or lowered by engaging the handle 11 secured to the lower portion of the door which is comprised of a plurality of horizontally hinged sections 12. Adjacent sections of the door 10 are connected by hinges 13 (FIG. 10) in a substantially conventional manner, and the sections are preferably fabricated from a fire-resistant material, such as steel, which is of sufficient'thickness to withstand intense heat for a specified period of time. In other respects, the door sections 12 may be substantially conventional, or they may be reinforced with fireproof material.

A pair of upright side seals or door braces 16 and 17 are mounted upon the interior surface of the wall 18 near to but spaced from the edges of the opening 19 in the wall 18, which opening is covered by the door 10. The door brace 16, for example (FIG. 2), is comprised in this particular embodiment of two angle members 22 and 23 which have two flanges thereof bolted together to provide a substantially S-shaped cross section. A sheet metal or plastic strip 4 is clamped between the flange 26 of the angle member 22 and the interior surface of the wall 18 by bolts 27 which extend through appropriate openings in the flange 26, the strip 24 and the wall 18. The bolt openings in the flange 26 and strip 24 are vertically elongated to allow for expansion or contraction relative to the wall 18. The strip 24 extends beyond the angle member 22 and is bent lengthwise thereof so that the inner edge portion 28 is spaced from the wall 18 for reasons appearing hereinafter. This metal strip 24 is preferably resiliently flexible.

The flange 29 (FIG. 2) of the angle member 23 ex tends inwardly, preferably approximately the. same' distance as the inward extent of the metal strip 24, to define a channel 32 into which the leftward edge of the door 10 is received and engaged by the edge portion 28. Thus, if the wall 18 is on the exterior of a building, then the strip 24 serves both as a weather strip and as a fire seal.

A pair of door guide tracks 33 and 34 (FIG. 2) are mounted upon the side seals 16 and 17, respectively, as appearing in FIGS. 1 and 2. Specifically, the guide track 33 is substantially channel-shaped incross section except that the rear flange 36 is bent frontwardly along its free edge to prevent accidental disengagement of the rollers 37 which move along the track '33. The guide track 33 is secured to the side seal 16 by elongated mounting strips 38 which, in this embodiment, are welded to the guide track 33 and bolted to the side seal 16 by the same bolts 39 which secure the angle members 22 and 23 together.

Each roller 37 is rotatably supported upon a shaft 42 which is in turn slideably supported by a bracket 43 mounted upon the interior side of the door 10. The shaft-supporting bracket 43 may be an integral part of the hinge 13 (FIG. 10), or the bracket 43 may be independent of the hinges as shown in FIG. 3 at 43B and in FIG. 4 at 43C. Moreover, additional hinges can be mounted upon the door as required or desired.

The roller brackets 43C (FIG. 4) are adjacent the upper edge of the upper section, and the roller brackets 43B (FIG. 3) are adjacent the lower edge of the lower section of the door to guide these sections.

The track 33 has a substantially upright'p'art 44 which is curved rearwardly at its upper end 47 preferably to define one-eighth of a circle. The guide track 33 also has a substantially horizontal part 45, the front end 48 of which is curved downwardly to define one-eighth of a circle. The free ends of the curved portions 47 and 48 are rigidly held together by a fusible connector 49 (FIG. 10) which is comprised of two parts secured to each other by solder which, in this embodiment, will melt at approximately 285F. Accordingly, when the two parts of the connector separate under intense heat, the track part 44 is thereupon completely separated from the track part 45. The horizontal part 45 of the track 33 may also be suspended from the ceiling 52, for example, by a hanger 53.

Under some circumstances, it may be desirable to locate the horizontal part 45 from seven to twelve inches above the lintel 54 (FIG. 5), particularly where the ceiling 52 is low.,In other cases, where the ceiling permits, the horizontal part 45 may be 2 feet or more above the lintel. In such case, the length of the upright part 44 of the track '33 is increased and the length of the horizontal part 45 can be decreased proportionately. That is, a greater part of the door can remain in a substantially vertical plane when the door is open.

Where there is adequate headroom, it may be unnecessary to have any horizontal part in the track 33. That is, the upright part 44 simply extends upwardly along the wall 18 sufficiently to accommodate the door 10 both in its closed and opened positions.

As shown in FIG. 5, the side seal 16 terminates somewhat below the lintel 54 to permit the sections 12 of the door to make the turn around the curved portions 47 and 48 where the horizontal part 45 of the track must be maintained at a low level. Thus, the upper end 47 of the upright part 44 is connected by rivets 56 to the mounting member 57 which is in turn secured to the interior surface of the wall 18 by bolts 58. One end of the counterbalance mechanism 61 (FIG. 6), which is discussed hereinafter, is also supported upon the mounting member 57.

The side seal 17, the metal strip 24A, the guide track 34, the roller 37A, the bracket 43A and the various parts associated therewith, and located on the other side (FIG. 2) of the opening 19, may be, and preferably are, substantially identical with or mirror images of the corresponding parts discussed above. Accordingly, a detailed discussion'of these parts, located on the right side of the opening 19, is believed unnecessary. The right side of the door 10 is received into the channel 32A where it is engaged by the metal strip 24A.

The roller shafts 42 and 42A (FIG. 2) are encircled by spiral springs 62 and 62A. The spring 62 is held under slight compression between the bracket 43 and integral projections 63 on the shaft 42. The spring 62A is held under slight compression between the bracket 43A and the projections 63A. Thus, the springs 62 and 62A tend to center the door between the side seals 16 and 17, and to prevent contact therewith. The rollers 37 and 37A hold the door 10 away from the flanges 29 and 29A.

Where the side seals 16 and 17 do not reach the top of the door opening as in the disclosed embodiment, overlapping and interlocking flanges or baffles 65 and '66 (FIG. 4) are mounted on the lintel 54 and upper end of the door 10, respectively. These interlocked flanges hold the upper end of the door securely and closely adjacent the wall 18 when the door is in its closed position. The flanges 65 and 66 which have substantially L- shaped cross sections and are preferably fabricated from heavy-gauge sheet metal also act as a seal against weather, air movement and fire movement. The flange 65 is secured to the lintel 54 by bolts 67 and the flange 66 is secured to the upper section of the door by rivets, welding or the like. I

In order to permit the use of standard door parts and/or existing tools in fabricating the fire door 10, an extension 68 (FIGS. 1 and 3) which has a substantially channel-shaped cross section, is mounted on the lower edge of the lowermost section of the door 10 to compensate for the raising of the upper section of the door to accommodate the overlapped flanges 65 and 66. That is, the extension 68 provides the additional amount of door required to permit the seal arrangement created by the flanges-65 and 66. The extension 68 is preferably made from relatively heavy-gauge sheet metal and also provides for an adjustment of the lower edge of the door to permit snug engagement of the threshold 69 when the door is in its closed position.

The counterbalance 61 (FIG. 6) includes a pair of coaxial shafts 72 and 73 which are connected at their turn supported upon the flanged mounting plates 78 and.79. The flanges on the front ends of the plates 78 and 79 are secured to the interior surface of the wall 18 by bolts 80 and 80A, respectively. The remoteends of the shafts 72 and 73 are rotatably supported by the bearings 82 and 82A (FIGS. 11 and 6), respectively, mounted on the mounting members 57 and 57A (FIG. 6). Locking collars 83 and 83A mounted upon said shafts 72 and 73, respectively, near their remote ends restrict axial movement-of said shafts with respect to said mounting members 57 and 57A.

A pair of cable drums 84 and 84A are mounted upon and secured to the shafts 72 and 73, respectively, adjacent to and between the mounting members 57 and 57A. Each of the cables 86 and 86A is secured at one end to one of the cable drums 84 and 84A, respectively, and at the other end to the lower section of the door 10, as shown in FIG. 3.

A pair of spiral springs 87 and 87A encircle the shafts 72 and 73, respectively. The spring 87 is connected at its outer end to a flanged collar 88 which in turn is secured by the set screws 89 to the shaft 72. The inner end of the spring 87 is secured to a flanged collar 92 (FIG. 9), which is rotatably supported upon the shaft 72 by the bearing 93. A tension wheel 94 is secured to the inner axial end of the collar 92 by bolts Flanged collars 88A and 92A are secured to the opposite ends of the spring 87A and mounted upon the shaft 73 in the same manner as described above with respect to their counterparts on the shaft 72. A tension wheel 97 is mounted upon the inner axial side of the flanged collar 92A by bolts 98. The tension wheel 97 has a plurality of integral, axially extending lugs 101 (FIG. 8) which are located at spaced intervals around the tension wheel, and each lug has a radially disposed opening 102 (FIG. 6). A bar 103 (FIG. 8)'is rigidly secured, as by welding, to the tension wheel 97 between two lugs 101 and extends radially beyond the periphery thereof. I

A pawl shaft 104 (FIGS. 8 and 9) is rotatably supported upon, and extends through openings in, the mounting plates 78 and 79. A pawl 106 is pivotally supported at one end upon the shaft 104 in radial alignment with the tension wheel 97.. The pawl 106 (FIG. 8) has an offset between its ends which provides an upwardly facing shoulder 107 when the pawl 106 is suspended from the shaft 104. The shoulder 107 is engageable by the bar 103 to limit positively clockwise rotation of the tension wheel 97, as appearing in FIG. 18.

A pawl 108 (FIG. 9), which is preferably identical with the pawl 106, is mounted upon the other end of the pawl shaft 104in radial alignment with the tension wheel 94 for engagement by a bar mounted on the tension wheel in the manner discussed above with respect to the bar 103 on the tension wheel 97 An ear 109 (FIG. 8) is lanced and bent out of the mounting plate 79 in a position just above the location of the bar 103 when it is engaging the shoulder 107. The ear 109 is positioned so that it will be struck by the bar 103, thereby limiting rotation of the tension wheel 97 to less than 360. under normal operating conditions. An ear 112 (FIG. 6) is lanced out of the mounting plate 78 is substantially the same manner and for substantially the same purpose as discussed above with respect to the ear 109.

An angle member 113 (FIG. 6) is secured to andextends between the lower rearward comers of the mounting plates 78 and 79, and an eyebolt 114 (FIG. 7) is anchored on the angle member 113 so that the eyelet thereof extends downwardly and frontwardly from the member 113. An angle member 116 (FIG. 8) is secured by bolts 117 to, and extends between the lower ends of, the pawls 106 and 108. Thus, the two pawls are required to pivot simultaneously.

A fusible link us is connected between the eyebolt 114 and the angle member 116 by apair of S-shaped I hooks 119. The link 118 is fabricated from a material having a melting point of approximately F. The length of the link 118 and hooks 119 is such that they hold the pawls 106 and 108 in position for engagement by the bar 103 and a corresponding bar on the tension wheel 94, respectively.

As shown in FIG. 8, the shoulder 107 is rearwardly of I a dead-center position directly below the pawl 104 when the pawl 106 is engaged by'the bar 103. Ac-

cordingly, if the link 118 is ruptured, the pawl 106- tube 124 which, as shown in FIG. 6, is supported upon the upper edge of the mounting plate 79 by an angle member 126 secured thereto. Thus, when the link 118 ruptures and the pawl 106 is thereafter moved to one side, subsequent downward movement of the bar 103 pulls the cable 123 downwardly, hence, through the tube 124. 1

Before the link 118 can be repaired, it is necessary to return the tension wheels to their original positions, and this requires considerable force to increase the tension on the springs 87 and 87A. It is accomplished by inserting a long lever bar 120 (FIG. 8) into the opening in one of the lugs 101 and rotating the tension wheel 97 counterclockwise until another lug passes the ear 109, after which a pin 121 is inserted into said other lug and eased back against the ear. This procedure is repeated until the bar 103 is returned to its FIG. 8 position.

The governor 130 (FIGS. 6 and 12) is mounted upon and between the shaft 72 and the mounting member 57. Specifically, a support plate 131 is secured by bolts 132 to the upper portion of the mounting member 57 and extends upwardly therefrom. A ring 133 has a large coaxial opening 134 and an eccentric pivot opening 136 through which a shaft 137 extends for pivotally supporting the ring upon the support plate 131 to which the shaft 137 is rigidly secured.

A ratchet wheel 138 (FIG. 12) is mounted upon and rotatable with the shaft 72 within the ring 133. The

teeth 141 on the ratchet 138 are symmetrical,

uniformly spaced and each tooth has a pair of radially outwardly converging straight edges which substantially-define a right angle. The outer points of the teeth define a circle which is of slightly less diameter than the distance between the radially inward end of the integral tooth 142 on the ring 133 and the diametrically opposite side of said coaxial opening. Thus, the ratchet wheel 138 can rotate with respect to the ring 133 and within the ring 133 without causing engagement between the tooth 142 and any of the teeth 141. However, in order to permit such rotation, the ring 133 must be held slightly sidewardly of its normal depending position when freely supported by the pivot shaft 137.

A pawl 143 (FIG. 12) is pivotally supported by a shaft 144 within the radially disposed slot 146 which extends completely through the ring 133. A spring 147 is secured between an integral hook 148 on the pawl 143 and a pin 149 which extends across the slot 146 and is secured to the ring 133. An adjustment screw 152 extends through an integral flange 153 which projects slightly over the slot 146. The screw 152 is located to engage an arm 154 on the pawl 143 to limit movement of the pawl toward the ratchet wheel 138.

A rod 156 having an eyelet on one end thereof extends through a pair of aligned openings 157 in the ring 133 on opposite sides of the slot 146. The openings 157 are located so that the arm 154 will be held by the rod away from the adjustment screw 152, contrary to the urging of the spring 147. The rod 156 also extends through an opening in the support plate 131 whereby the ring 133 is held in said sideward position wherein the ratchet wheel 138 can rotate without interference from the tooth 142 or any other part on the ring 133.

The outer end of the rod 156 has an integral eyelet to which the other end of the cable 123 is attached. Accordingly, when the fusible link 118 ruptures, as discussed above, downward movement of the cable 123 by bar 103 causes it to pull the rod 156 out of engagement with the ring 133, whereby the pawl 143 is urged by spring 147 to engage the ratchet wheel 138 and thereby move the tooth 142 into engagement with one or a pair of the teeth 141. By oscillating back and forth, under the urging of spring 147, and acting through the tooth 142, the teeth 14] and the pawl 143, the shaft 72 is permitted to rotate in a step-by-step movement under the urging of the downward pull of the cable 86 acting on the drum 84 whereby the door closes due to gravity. Such rotation of the drum under the urging of the cable will result from the fact that some of the tension has been removed from the spring 87 by the rotation of the tension wheel 94 after the fusible link 1 18 ruptures.

The end of the cable 123 secured to the rod eyelet 158 is also connected to one end of a spiral spring 159, the other end of which is hooked onto the support plate 131. Accordingly, when the rod 156 is pulled out of engagement with ring 133, the rod is held close to the governor for easy retrieval and reinsertion into the ring when the fusible link 118 has been replaced.

ALTERNATE STRUCTURE The door assembly disclosed above is designed for direct manual operation by grasping the .handle 11' and either raising or lowering the door in the usual manner. However, where the door is large and/or heavy, it is advantageous to operate same with a chain-and-gear system or by a power-driven door operator, both of which may be substantially conventional.

For example, FIG. 14 illustrates an actuating mechanism which is mounted upon the outer end of the shaft 73B, which may be identical with the shaft 73 of FIG. 6. Specifically, a large gear 166 is mounted upon and rotatable with the outer end of the shaft 73B. A support plate 167 is secured by bolts 168 to the mounting member 57B (FIGS. 15 and 16) and projects rearwardly beyond the rearward edge of the said member 573. A pawl 169, which may be identical with the pawl 106, is pivotally supported by the shaft 172 upon the rear end of the support plate 167 and has an upwardly facing shoulder 173 projecting toward the mounting member 57B.

A lever arm 174 (FIG. 15) is pivotally supported upon a pivot shaft 176 located below the gear 166 and rigidly secured'to the support plate 167. A small gear 177 is also rotatably supported upon the shaft 172 outward of the lever arm 174. A sprocket 17 8 is secured to the hub of the gear 177 for engagement by a long chain 179 suspended from the sprocket. An intermediate gear 182 is rotatably supported upon the lever arm 174 and is in continuous engagement with the small gear 177. By pivoting the lever arm 174 upwardly, the intermediate gear 182 can also be brought into toothed engagement with the large gear 166. When the outer free end of the lever end 174 is resting upon the shoulder 173, all three gears are engaged.

The free end of the arm 174 (FIG. 15) is engaged by a hook 183 which is connected to one end of a cable 184 that extends upwardly through an eyelet 186 secured to the extended end of the support plate 167 adjacent the pivot shaft 172. The cable 184 then extends horizontally toward the wall 18 where it passes through an eyebolt 187 mounted on said wall. The cable 184 then extends downwardly through another eyebolt 188 on the wall 18 to a point where it can be manually engaged to reset the lever arm 174 on the shoulder 173 when it has been accidentally disengaged.

An eyebolt 191 (FIG. 15) is connected to the lower end of the pawl 169 and is connected to a hook 192. Another hook 193 is connected to a cable 194 which extends horizontally toward the wall 18 and then upwardly through the eyebolts 188 and 187, and thence through an eyebolt 196 mounted in the ceiling.

The cable 194 extends from eyebolt 196 through eyebolt 197 (FIG. 17) andthen down through guides 198 and 199 on the angle members 126 and 113, respectively. Finally, the end of the cable 194 is secured to the angle member 116. In this embodiment, the fusible link 118 (FIG. 8), the eyebolt 114 and the hooks 119 are eliminated.

Instead, the hooks 192 and 193 (FIG. are intercorinectedby a fusible link 202 which, like the fusible link 118, is made of metal or other material which has reasonably strong tensile strength but will melt at approximately 160F. It will be apparent that when the link 202 breaks (FIGS. 15 and 16),.the pawl 169 will swing away from the lever arm 174 thereby permitting the lever arm to move downwardly and disconnect the intermediate gear 182 from the large gear 166. At the same time, the tension is released on the cable 194, whereby the tension is removed from the springs 87 and 87A and the door 10 cannow move downwardly under the force of gravity.

OPERATION prevent such falling away of the upper section of the door, there is really no need to increasethe lengths of the upright parts 44 and 44A beyond those disclosed in the drawings.

In the'principal embodiment illustrated herein, the

I door can be opened manually by grasping the handle While the operation of the above-described fire door assembly willbe evident to skilled persons in this field from an examination of such description, the operation will now be summarized for convenience.

Starting with the door 10in its closed, solid line position of FIGS. 1 and 5, said door will be disposed within the channels 32 and 32A (FIG. 2) defined by the side seals 16 and 17, and the metal weather strips 24 and 24A, respectively. It will be apparent that the metal strips 24 and 24A, under some circumstances, may be omitted whereupon the adjacent portions of the wall 18 provide the front sides of the charmels. The lower edge of the lowermost section 12 in the door, which edge is provided by the extension 68 in this embodiment, will be in contact with the threshold 69, so that the escape of air and/or fire around the side edges or under the bottom of the door is positively prevented.

The upper edge of the uppermost section of the door 10 will be held closely adjacent the wall 18 by the overlapped portions of the flanges 65 and 66 secured to the lintel 54 and upper edge of the door 10, respectively.

The overlapped flanges 65 and 66 will also positively oppose the escape of air or fire between the upper edge of the door and the wall 18.

Although the side seals 16 and 17 stop short of the upper edge of the opening 19, the flanges 65 and 66 will hold the upper section of the door 10 close to the wall 18 so that the amount of air which escapes between the upper portion of the door and the wall 18 is minimal at most. Moreover, since the door overlaps the wall, there is no reasonable chance for flame or fire to move between the ends of the upper section of the door and the adjacent part of the wall.

However, if desired, the upright parts 44 and 44A of the guide tracks 33 and 34, respectively, can be lengthened so that the side seals can also be lengthened without interfering with the downward movement of the door. Since the principal function of the side seals 16 and 17 is to hold the door in place against the wall under intense heat, and since the flanges 65 and 66 11 (FIG. 1) and raising it whereby one section after another moves from the upright parts of the tracks'33 and 34 onto and along the horizontal parts thereof. The tension on the counterbalance springs 62 and 62A (FIG. 6) is gradually reduced as the cables 86 and 86A are wound upon the cable drums 84 and 84A, respectively. When the door is in its fully raised position, as shown in FIG. 5- at 10A in broken lines, the tension on the springs 62 and 62A is only sufl'icient to prevent the door from sliding down the tracks 33 and 34 back into the closed position under the force of gravity. When it becomes desirable to close the door 10, the handle 11 must be manually grasped and the door must be pulled downwardly into the closed position in the usual manner. Thus, during normal use of the door, it

operates in substantially the same manner as any other door of the upwardly acting type, and some tension in the springs must be physically overpowered.

If a fire occurs within the zone defined by the interior surface of the wall 18 and, further, if the temperature in V the region of the door reaches approximately 160 for a timesufficient to melt the fusible link 11 8 (FIG. 8), the link will rupture and permit the tension wheels 94 and 97 to push the pawls 108 and 106 out of their way so that the tension wheels can rotate almost one revolution, or until they strike the ears 112 and 109. This releases an amount of tension on the springs 87 and 87Awhichwill permit the drums 84 and 84A torotate and'release a substantial amount of cable therefrom, whereby the lower edge of the door is permitted to slide down along the guide tracks 33 and 34. Even though the tension in the springs 87 and 87A continues to increase while the cable thereafier unwinds from the drums, the initial reduction in tension .in the springs is such that gravity'can overcome the increased tension and, accordingly, the door will go into the fully closed position. I

When the fusible link 118 ruptures, the cable 123 will be pulled downwardly (FIG. 8) whereby it will v has been melted by a localized source of heat which has not damaged the door 10 beyond minor repair, the door can be promptly returned to service in its initial arrangement by inserting the lever bar 120 in anopening 102 (FIG. 6) in one of the exposed lugs 101 and thereby forcing rotation of the tension wheel 97 (or the tension wheel'94) in a step-by-step movement. That is,

after the tension wheel has been rotated far enough for one of the lugs 101 (FIG. 8) to move in a counterclockwise direction past the ear 109, a small pin 121 can be inserted into that particular lug and the tension wheel permitted to rotate in a clockwise direction until such pin engages the ear 109 and thereby prevents further clockwise rotation. The bar 120 can then be placed in the adjacent lug, in a counterclockwise direction, and the tension wheel can be rotated until the next lug in a clockwise direction passes the ear 109 after which the procedure of using the pin is repeated.

In the foregoing manner, the tension wheel 97, for example, is rotated until the lug 101 next to the bar 103 in a counterclockwise direction contains the pin 121, which bears against the ear 109. In this position, the bar 103 will be slightly above the position of the shoulder 107 when the pawl 106 is returned to its FIG. 8 position. Accordingly, a new fusible link 118 can be attached between the angle member 116 and the eyebolt 114 without having to exercise force to hold the pawl 106 in its proper position. The bar 120 can now be used to move the tension wheel 97 back in a counterclockwise direction so that the pin 121 can be removed from the lug adjacent the ear 109, after which the bar 103 is then eased down into engagement with the shoulder 107 whereby the tensioning operation is completed.

The governor can now be returned to its detent position by pivoting the ring 133 into its ofl-center position of FIG. 12 after which the pawl 143 is rotated into its FIG. 12 position against the contrary urging of the spring 147. The rod 156 is then moved through the support plate and inserted through the openings 157 in the ring 133, whereby the pawl 143 and the ring 133 are held in their detent positions which prevent interference thereby with the rotation of the ratchet wheel 138.

Thus, with the tension wheels and governor returned to their original operating conditions, normal operation of the door can be carried out and, moreover, the door assembly is again ready to close automatically in case of a fire.

The alternate arrangement (FIG. 14), which includes the chain-operated mechanism for opening and closing the door, has a fusible link 202 (FIG. 15) which, when ruptured, releases the pawl 169 so that the intermediate gear 182 can be automatically disengaged from the large gear 166. This permits the shafts 72 and 73 to rotate without any interference from the gear train including the large gear 166. Otherwise, the frictional resistance created by the gear train would normally be sufficient to prevent downward movement of the door under the force of gravity, even if the tension on the springs 87 and 87A is released, as discussed above.

While the fusible link 202 is ruptured, the cable 194 is also released sufficiently to permit the tension wheels 94 and 97 to escape the pawls 108 and 106 and thereby release tension from the springs and, at the same time, actuate the governor 130 in the same manner. as discussed above.

Under some circumstances, it may be desirable, particularly with very large and heavy doors, to connect the small gear 177 to a prime mover, such as a reversible electrical motor, through a gear box having a slow speed output. The actuating mechanism 165 could be substantially the same as discussed above, except that the small gear 177 would be driven by a motor instead of by a chain and sprocket.

Since the shafts 72 and 73 are connected by a flanged coupling 74, failure of one of the cables 86 and 86A or failure of one of the springs 87 and 87A would not eliminate all of the counterbalancing effect. That is, even one spring and one cable intact would prevent the door from applying an overload to the governor 130.

Because of the fusible connector 49 between the upright part 44 and the horizontal part 45 of the guide track 33, for example, an intense fire near the door 10 would separate said parts 44 and 45 from each other in a relatively short period of time. Thus, if the fire became so intense as to collapse the roof of the building, and thereby drag the horizontal parts of the tracks 33 and 34 downwardly, they would have been separated from the upright parts of the tracks and, accordingly, cannot rip the door 10 away from the wall.

The depths and widths of the channels 32 and 32A (FIG. 2), and the clearances between the lateral edges of the door and the elements defining the channels 32 and 32A are such that they provide adequate room for expansion due to elevated temperatures to which they might be subjected by direct contact with flames or intense heat.

By mounting the upright parts of the tracks 33 and 34 outside the guide channels 32 and 32A, a failure in the performance of theyrollers 37 and 37A will not interfere with the emergency movement of the door along the channels 32 and 32A.

Although particular preferred embodiments of the invention have been disclosed above for illustrative purposes, it will be recognized that variations or modifications of the disclosed structure, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A door assembly for covering an opening in an upright wall, comprising:

door means having plural, horizontally hinged sections;

brace means secured to said wall adjacent the opening therein and defining a pair of upright channels opening toward each other and arranged to receive opposite edge portions of said door; pair of L-shaped track means rigidly held with respect to said brace means, said track means having upright portions adjacent said brace means and parallel, horizontal portions extending away from said brace means in the same direction, said horizontal portions and upright portions having adjacent, arcuate portions; roller means on said door sections and engaged with said track means for guiding movement of said door means between a closed position within said channels and a horizontal, open position; spring-biased counterbalance means mounted on said wall above said opening and having drum means supporting cable means connected to the lower part of said door means, and spring means continuously resiliently urging said drum means to rotate in a cable-winding direction whereby said door means is continuously resiliently urged toward said open position; and fusible link means connected to said spring means for maintaining a predetermined minimum tension thereon whereby rupture of said link means permits release of at least a part of the tension in said spring means to enable said door means to move by gravity from said open position into theclosed position. I V 2. A door assembly according to claim 1, wherein said door means and said brace means are fire resistant; wherein said counterbalance means includes horizontal shaft means supported upon said wall means, said drum means being mounted upon and rotatable with said shaft means, and said spring means being a spiral spring having one end thereof secured to said shaft means; and including pawl means pivotally mounted upon said wall means and engageable with the other end of said spiral spring for holding same against rotation, said pawl means being releasably held in said position of engagement by said fusible link means.

3. A door assembly according to claim 1, wherein said counterbalance means includes shaft means to which said drum means is secured, and said spring means includes a spiral spring having one end secured to said shaft means and the other end thereof releasably held with respect to said wall means;

including sprocket means rotatably supported upon said wall means near one end of said shaft means; chain means engaged with said sprocket means for rotating same; i

arm means having one end pivotally supported upon said wall means adjacent to and coaxial with said sprocket means;

gear means connecting said sprocket means to said shaft means, said gear means including a first gear onsaid shafl means and a second gear supported on said arm means for movement with said arm means into and out of engagement with said first gear; and wherein said fusible link means holds said arm means in a position for engagement between said first and second gears. 4. A door assembly for covering an opening in an upright wall, comprising: door means having plural, horizontally hinged sections; brace means secured to said wall adjacent the opening therein and defining a pair of upright channels opening toward each other and arranged to receive opposite edge portions of said door means;

a pair of L-shaped track means rigidly held with respect to said brace means, said track means having upright portions adjacent said brace means and parallel, horizontal portions extending away from said brace means in the same direction, said horizontal portions and upright portions having adjacent, arcuate portions;

roller means on said door sections and engaged with said track means for guiding movement of said 'door means between a closed position within said channels and a horizontal, open position; spring-biased counterbalance means mounted on said wall above said opening and having drum means supporting cable means connected to the lower part-of said door means, said counterbalance means including shaft means to which said drum means is secured, and spring means resiliently urging said drum means to rotate in a cable-winding direction, said spring means including a spiral spring having one end secured to said shaft means and the other end thereof releasablyv held with respect to said wall means;

sprocket means rotatably supported upon said wall means near one end of said shaft means;

chain means engaged with said sprocket means for rotating same; I A

arm means having one end pivotally supported on said wall means adjacent to andcoaxially with said sprocket means;

gear means connecting said sprocket means to said shaft means, said gear means including a first gear on said shaft means anda second gear supported on said arm means for movement with said arm means into and out of engagement with saidfrrst gear; and v a fusible link means connected to said spring means for maintaining a predetermined tension thereon whereby ruptureof said link means permits release of at least a part of the tension in said spring means to enable said door means to moveby gravity into the closed position, said fusable link means holding said arm means in a position for engagement between saidfirst and second gears.

5. A door assembly according to claim 4, including governor means connected between said shaft'means and said wall means for limiting the rotational speed of said shaft means;

releasable holding means for maintaining saidgovernor means in an inoperative position;

linkage means interconnecting said holding means and said fusible link means for releasing said holding means when said fusible link means ruptures, whereby said governor means becomes operative.

6. A door assembly according to claim 4, wherein said fusible link means includes pawl meam releasably engageable with said arm means in said engaging posi tion; and

a fusible link connecting said pawl means to said linkage means. i

7. In a fire door assembly having a horizontally sec tioned door supportedby track means for movement between a substantially upright closed position and a substantially horizontal opened position and springbiased counterbalance'means for holding said door in an openposition, said counterbdance means including drum means and cable means extending between said drum means and the lower part of said door, and fusible I link means for releasing the tension on said counterbalance means whereby said door canmove by gravity from its opened position into its closed position automatically, governor means for controlling the movement of said door, comprising:

toothed wheel means secured to and rotatable with said drum means; annular means encircling said wheel means and pivotally supported at a point directly above the axis of said wheel means for movement around an.

axis parallel with said wheel axis; projection means extending radially inwardly from the inner surface of said annular means and being engageable with the teeth on said wheel means,

when said annular means is coaxial with said wheel means; a

pawl means pivotally supported upon said annular means and resiliently urged into engagement with said teeth, whereby said annular means is caused to pivot as said wheel means rotates in a step-bystep movement and said projection means moves into and out of engagement with successive teeth; and

pin means releasably holding said annular means eccentric with respect to said wheel means and holding said pawl means out of engagement with said teeth, whereby said wheel means can rotate independently thereof.

8. A fire door assembly mountable upon wall means having a substantially vertically extending opening therein, comprising:

door means having a plurality of horizontally hinged sections;

track means mountable upon said wall means and supporting said door means for movement between an upright closed position wherein said door means is disposed adjacent said opening and a substantially horizontal opened position, said track means including an elongated track portion disposed substantially horizontally and extending transversely relative to said opening for supporting said door means when same is in said opened position',

spring-biased counterbalance means adapted for mounting on said wall means and connected to the lower portion of said door means and including spring means for continuously resiliently urging said door means toward said horizontal opened position; and

linkage means including a fusable link connected to said counterbalance means and adapted to rupture at a predetermined temperature to release at least a part of the tension in the spring means to enable said door means to automatically move from its opened position to its closed position under the force of gravity.

9 A door assembly according to claim 8, further including power means releasably connected to said door means for permitting powered movement of said door means between said opened andclosed positions, and said linkage means being interconnected to said power means for disconnecting said power means from said door means whenever said'fusable link ruptures for permitting said door means to freely move from the opened position to the closed position under the force of gravity.

10. A door operator according to claim 8, wherein said spring-biased counterbalance means includes horizontal shaft means supported on said wall means adjacent the upper edge of said opening, rotatable drum means supported on said shaft means, elongated flexible element means connected between said drum means and the lower edge of said door means, said spring means including a torsion spring disposed adjacent said shaft means and having one end thereof fixedly connected relative to said drum means for continuously resiliently urging same in a rotational direction tending to move said door means to said opened position, and disk means mounted on said shaft means and supported for rotation relative to said wall means, said disk means being fixedly interconnected to the other nd of said torsio s ring; and

said age means incu ng movable link means coating between said disk means and said wall means for normally releasably maintaining said disk means stationary relative to said wall means, said link means being automatically disengaged from said disk means on rupture of said fusible link for enabling said disk means to rotate relative to said wall means to at least partially release the tension in said torsion spring. 

1. A door assembly for covering an opening in an upright wall, comprising: door means having plural, horizontally hinged sections; brace means secured to said wall adjacent the opening therein and defining a pair of upright channels opening toward each other and arranged to receive opposite edge portions of said door; a pair of L-shaped track means rigidly held with respect to said brace means, said track means having upright portions adjacent said brace means and parallel, horizontal portions extending away from said brace means in the same direction, said horizontal portions and upright portions having adjacent, arcuate portions; roller means on said door sections and engaged with said track means for guiding movement of said door means between a closed position within said channels and a horizontal, open position; spring-biased counterbalance means mounted on said wall above said openiNg and having drum means supporting cable means connected to the lower part of said door means, and spring means continuously resiliently urging said drum means to rotate in a cable-winding direction whereby said door means is continuously resiliently urged toward said open position; and fusible link means connected to said spring means for maintaining a predetermined minimum tension thereon whereby rupture of said link means permits release of at least a part of the tension in said spring means to enable said door means to move by gravity from said open position into the closed position.
 2. A door assembly according to claim 1, wherein said door means and said brace means are fire resistant; wherein said counterbalance means includes horizontal shaft means supported upon said wall means, said drum means being mounted upon and rotatable with said shaft means, and said spring means being a spiral spring having one end thereof secured to said shaft means; and including pawl means pivotally mounted upon said wall means and engageable with the other end of said spiral spring for holding same against rotation, said pawl means being releasably held in said position of engagement by said fusible link means.
 3. A door assembly according to claim 1, wherein said counterbalance means includes shaft means to which said drum means is secured, and said spring means includes a spiral spring having one end secured to said shaft means and the other end thereof releasably held with respect to said wall means; including sprocket means rotatably supported upon said wall means near one end of said shaft means; chain means engaged with said sprocket means for rotating same; arm means having one end pivotally supported upon said wall means adjacent to and coaxial with said sprocket means; gear means connecting said sprocket means to said shaft means, said gear means including a first gear on said shaft means and a second gear supported on said arm means for movement with said arm means into and out of engagement with said first gear; and wherein said fusible link means holds said arm means in a position for engagement between said first and second gears.
 4. A door assembly for covering an opening in an upright wall, comprising: door means having plural, horizontally hinged sections; brace means secured to said wall adjacent the opening therein and defining a pair of upright channels opening toward each other and arranged to receive opposite edge portions of said door means; a pair of L-shaped track means rigidly held with respect to said brace means, said track means having upright portions adjacent said brace means and parallel, horizontal portions extending away from said brace means in the same direction, said horizontal portions and upright portions having adjacent, arcuate portions; roller means on said door sections and engaged with said track means for guiding movement of said door means between a closed position within said channels and a horizontal, open position; spring-biased counterbalance means mounted on said wall above said opening and having drum means supporting cable means connected to the lower part of said door means, said counterbalance means including shaft means to which said drum means is secured, and spring means resiliently urging said drum means to rotate in a cable-winding direction, said spring means including a spiral spring having one end secured to said shaft means and the other end thereof releasably held with respect to said wall means; sprocket means rotatably supported upon said wall means near one end of said shaft means; chain means engaged with said sprocket means for rotating same; arm means having one end pivotally supported on said wall means adjacent to and coaxially with said sprocket means; gear means connecting said sprocket means to said shaft means, said gear means including a first gear on said shaft means and a second gear supported on said arm means foR movement with said arm means into and out of engagement with said first gear; and fusible link means connected to said spring means for maintaining a predetermined tension thereon whereby rupture of said link means permits release of at least a part of the tension in said spring means to enable said door means to move by gravity into the closed position, said fusable link means holding said arm means in a position for engagement between said first and second gears.
 5. A door assembly according to claim 4, including governor means connected between said shaft means and said wall means for limiting the rotational speed of said shaft means; releasable holding means for maintaining said governor means in an inoperative position; linkage means interconnecting said holding means and said fusible link means for releasing said holding means when said fusible link means ruptures, whereby said governor means becomes operative.
 6. A door assembly according to claim 4, wherein said fusible link means includes pawl means releasably engageable with said arm means in said engaging position; and a fusible link connecting said pawl means to said linkage means.
 7. In a fire door assembly having a horizontally sectioned door supported by track means for movement between a substantially upright closed position and a substantially horizontal opened position and spring-biased counterbalance means for holding said door in an open position, said counterbalance means including drum means and cable means extending between said drum means and the lower part of said door, and fusible link means for releasing the tension on said counterbalance means whereby said door can move by gravity from its opened position into its closed position automatically, governor means for controlling the movement of said door, comprising: toothed wheel means secured to and rotatable with said drum means; annular means encircling said wheel means and pivotally supported at a point directly above the axis of said wheel means for movement around an axis parallel with said wheel axis; projection means extending radially inwardly from the inner surface of said annular means and being engageable with the teeth on said wheel means when said annular means is coaxial with said wheel means; pawl means pivotally supported upon said annular means and resiliently urged into engagement with said teeth, whereby said annular means is caused to pivot as said wheel means rotates in a step-by-step movement and said projection means moves into and out of engagement with successive teeth; and pin means releasably holding said annular means eccentric with respect to said wheel means and holding said pawl means out of engagement with said teeth, whereby said wheel means can rotate independently thereof.
 8. A fire door assembly mountable upon wall means having a substantially vertically extending opening therein, comprising: door means having a plurality of horizontally hinged sections; track means mountable upon said wall means and supporting said door means for movement between an upright closed position wherein said door means is disposed adjacent said opening and a substantially horizontal opened position, said track means including an elongated track portion disposed substantially horizontally and extending transversely relative to said opening for supporting said door means when same is in said opened position; spring-biased counterbalance means adapted for mounting on said wall means and connected to the lower portion of said door means and including spring means for continuously resiliently urging said door means toward said horizontal opened position; and linkage means including a fusable link connected to said counterbalance means and adapted to rupture at a predetermined temperature to release at least a part of the tension in the spring means to enable said door means to automatically move from its opened position to its closed position under the force of gravity.
 9. A door assembly according to claim 8, further including power means releasably connected to said door means for permitting powered movement of said door means between said opened and closed positions, and said linkage means being interconnected to said power means for disconnecting said power means from said door means whenever said fusable link ruptures for permitting said door means to freely move from the opened position to the closed position under the force of gravity.
 10. A door operator according to claim 8, wherein said spring-biased counterbalance means includes horizontal shaft means supported on said wall means adjacent the upper edge of said opening, rotatable drum means supported on said shaft means, elongated flexible element means connected between said drum means and the lower edge of said door means, said spring means including a torsion spring disposed adjacent said shaft means and having one end thereof fixedly connected relative to said drum means for continuously resiliently urging same in a rotational direction tending to move said door means to said opened position, and disk means mounted on said shaft means and supported for rotation relative to said wall means, said disk means being fixedly interconnected to the other end of said torsion spring; and said linkage means including movable link means coating between said disk means and said wall means for normally releasably maintaining said disk means stationary relative to said wall means, said link means being automatically disengaged from said disk means on rupture of said fusible link for enabling said disk means to rotate relative to said wall means to at least partially release the tension in said torsion spring. 